Means for automated comparison of two texts are well known in the art and widely used. These include, for example, means for comparing an original document and a revised document and visually marking text that changes between them. For the case of two documents, this may be accomplished with two visual styles: one for text in the original document that does not appear in the revised document (i.e. deleted text) and one for text in the revised document that does not appear in the original document (i.e. inserted text). Text that does not change from the original document to the revised document need not be separately marked.
For example, consider the following documents:
Document 1Document 2Our story starts on a dark andOur tale begins on a dark andstormy night many years ago,stormy night not many years ago,in an unremarkable house onin a nondescript house on anan unremarkable street inaverage street in anan unremarkable city.unremarkable city.
Assuming that Document 1 is the original document and Document 2 is the revised document, changed text might be marked with a visual style in which strikethrough signifies text from Document 1 that was deleted in Document 2, underline signifies text not contained in Document 1 that has been inserted into Document 2 and text unchanged between Document 1 and Document 2 is not marked. The results could be depicted as follows:
Document 1 Document 2Our story starts on a dark and Our     tale begins on a dark and stormy night many years ago, stormy night not many years ago, in   in an unremarkable house on   a nondescript house on an an unremarkable street in an   average street in an unremarkable city. unremarkable city.
Such pairwise document comparison systems (comprising means for comparing an original and a revised document and visually marking the results) are widely used. However, performing simultaneous comparison and visual marking of revisions with respect to more than two documents is more complicated.
As already noted, all changes between an original and a revised document may be reflected with only two visual marking styles: one for deleted text and one for inserted text. Reflecting changes between and among more than two documents requires an augmented system of visual marking because of a larger number of possibilities. In the case of three documents, for example, there are at least the following possibilities: i) text may be the same in all three documents; ii) text may be the same in Document 1 and Document 2, but not Document 3; iii) text may be the same in Document 1 and Document 3, but not Document 2; iv) text may be the same in Document 2 and Document 3, but not Document 1; v) text may differ in all three documents. Furthermore, possibilities (ii)-(v) each embed further permutations in the form of deletions, insertions or some combination thereof. Accordingly, a need has arisen for means for comparing, and generating revision markings with respect to, an arbitrary number of text segments.